why doesn't hand off work with my iMac macbook air and iOS devices
iMac, OS X Yosemite (10.10.3)
See this link for Handoff system and hardware requirement.
System requirements for Continuity on iPhone, iPad, iPod touch, and Mac - Apple Support
You would have to be a bit more specific about what is not working. Are the devices and the Mac all signed into the same iCloud account? Are the iOS devices running iOS 8 or higher? It appears that your Mac is running Yosemite, correct?
Have you checked Settings>General>Handoff on your devices to make sure it is turned on?
Cheers,
GB
Why doesn't handoff work
